Electronic systems generally include test points on which the performance of selected sections can be characterized. The need in such tests grows with the complexity of the system. Small (nanoscale, and in particular molecular level) devices, especially complex heterostructures grown as a single component, raise demanding requirements on the electrical measurements in these devices.
The existing electrical measuring tools, typically utilizing an electrodes' arrangement, cannot probe selectively the inner regions of such structures. These tools typically detect an integral signal, associated with a spatial region in between two (or more) attached electrodes. This fact limits the (electrical) resolution both vertically and laterally. Therefore, even the finest solid-state electrodes are practically incapable of measuring at the sub-molecular scale. The existing developments in this technical field thus present a principal problem in both accessing the inner components of a structure under electrical measurements, and in achieving enhanced spatial (electrical) resolution.
The electric contact to a given surface is frequently a serious problem by itself, introducing a new unknown interface with unknown electric properties. In various recently developed systems, which consist of fine structural variations close to the very surface, an attached contact may even affect the system directly. This difficulty can be answered efficiently by non-contact tools.
Recently, a new method for non-damaging depth profiling in the 15 nm range has been demonstrated [1]. This method is based on controlled surface charging (CSC) [1,2] in X-ray photoelectron spectroscopy (XPS). XPS is a powerful surface analytical tool, providing superior information on the chemical composition of surfaces and interfacial layers. The technique is based on illumination of the surface with X-rays and analysis of the photoelectrons ejected from the surface, thereby determining the identity and chemical state of atoms located on the surface and up to about 15 nm deep. In contrast to its nanometer-scale depth sensitivity, in the lateral direction XPS is essentially a macroscopic technique.
In the above-indicated method, as well as some other related techniques [3–5], the XPS line shifts, occurring upon charging, are used in order to extract position of atoms. Several works aimed at extracting qualitatively electrical aspects out of differential charging effects have been presented [6, 7].
U.S. 20020020814, assigned to the assignee of the present application, discloses an electron spectroscopy employing controlled surface charging. According to this technique, a sample is examined by performing a first spectroscopic analysis of a surface portion of the sample when the sample surface portion is in a first electrical charge state, placing the sample surface portion in a second electrical charge state that is different from the first electrical charge state and performing a second spectroscopic analysis of the surface portion of the sample when the sample surface portion is in the second electrical charge state. By comparing the first spectroscopic analysis result with the second spectroscopic analysis result at least one of structural and electrical information about the sample can be obtained.